Setting maxdsiz kernel parameter

[David Owens_1]

When setting the value for "maxdsiz", is it possible to set it too high based on the system resources (RAM & swap)? I am using some engineering applications that require the settings to be higher than the default so I selected "CAE/ME/General Eng. Workstation 64-bit Kernel" under the "Applied tuned parameter set" menu in SAM. After doing so, it fixed my initial problems but started a whole new subset of additioanl problems. It appears that now my application, Unigraphics, is not allocating memory very well. I have 1Gb of swap and 512 Mb of RAM on this workstation and the new values are:

maxdsiz=3221225472 (3,221,225,472)
maxdsiz_64bit=17179869184 (17,179,869,184)


David Owens

[A. Clay Stephenson]

Hi:

You need to note that these values are 'fences'. They consume no resources but are intended to keep rogue processes from grabbing all the memory in sight. Most CAD programs I am familiar with live very happily in about a 2GB 64bit maxdsiz. Of course, it is pointless, to let these values exceed (or even approach) your total virtual size. In that case, you are defeating their purpose. The idea is that it is better to allow the process to die rather than bringing the entire box to its knees. Fairly good 'large' 64-bit (these are the 64-bit values) workstation values are 1-2GB maxdsiz, maxssize 32MB (quite generous - if the programmer is allocation that size local variables he is doing it wrong); and maxtsiz 512MB. These are obviously starting point and 32-bit versions should drop maxdsize down to 1GB or so.

[Sridhar Bhaskarla]

Hi David,

Is your application a 64bit one?.

Your values seem to be too high. Try setting them low. Probably start with certain value like 500MB and keep increasing till you see a balance.

-Sri

[John Bolene]

My maxdsiz is 128Meg, had to bump it up from 64Meg default.

With your current physical memory size, I would not put it higher than 256Meg.

[A. Clay Stephenson]

Hi again,

I have not used Unigraphics but Pro/E, Mechanica, Ansys, Fluent, ... really, really bog down when you begin to swap. Your problem is not really the fence values but rather the amount of swapping you are asking the box to do when loading large models. If the price of memory from HP seems excessive then consider getting it from a used-equipment dealer or use 3rd party memory like Kingston. The real answer to your problem is to swap as little as possible. If your dbc_max_pct is over about 15%, you need to reduce it as well.

[Bill Hassell · Accepted solution]

As a general note, 512 megs is far, far too small to run a 64-bit kernel. The whole prupose in running 64 bits is to allow 64 bit programs to use massive amounts of RAM (gigabytes) and also allow 32 programs to use the max that they can (940 megs, 1750 megs or 2850 megs depending on compiler/loader/chatr options).

So 512 megs will keep you very busy trying to figure out how to manage applications like Unigraphics in such a small space. Changing maxdsiz to 3000 megs may have allowed Unigraphics to try to expand it's shared or data memory areas and there simply isn't enough space.

If you are constrained to 512 megs, try increasing swap space to 10 Gigabytes and see if the application runs. There may still be memory fragmentation in the shared area--use ipcs to look at the usage. While additional swap space can allow really large programs to run in a small RAM area, paging in and out of swap will just about cripple the program(s).

[Sanjay_6]

Hi David,

Here is a link to the kernel parameters,

http://docs.hp.com//hpux/onlinedocs/os/11i/kcparams/KCparams.OverviewAll.html

Here is the kernel parameter maxdsize,

http://docs.hp.com//hpux/onlinedocs/os/11i/kcparams/KCparam.MaxDsiz.html

Here are a few threads from ITRC on this kernel parameter,

http://us-support.external.hp.com/cki/bin/doc.pl/sid=cdf956a70398e91a62/screen=ckiDisplayDocument?docId=200000036013331

http://us-support.external.hp.com/cki/bin/doc.pl/sid=cdf956a70398e91a62/screen=ckiDisplayDocument?docId=200000049016694

Hope this helps.

Regds